Hydraulic axial piston pump able to operate in both directions

ABSTRACT

A hydraulic pump rotates in both directions of rotation, and includes a casing, a common drive shaft mounted so as to be able to rotate relative to the casing, two swashplates borne by the common drive shaft, these two swashplates being symmetric and opposite each other and each including one supply crescent, a respective hollow piston pressing against each swashplate via the intermediary of a slipper shoe and designed to slide in a respective cylinder connected to the casing, the crescent of the swashplate being in each case arranged so as to pass over the hollow piston during a suction phase of the hollow piston, each cylinder being fitted with a check valve on the discharge side, such that only one of the two swashplates provides an output when the drive shaft rotates in one direction, the other swashplate providing an output when the shaft rotates in the other direction.

The present invention relates to a hydraulic axial piston pump, in particular of small or very small displacement, which is able to operate in both directions of rotation so as to be able to actuate a hydraulic slave cylinder in one direction or the other.

It proves necessary to be able to actuate, for example in an oil drilling tube, a double-acting hydraulic cylinder without having to arrange a distributor in the hydraulic circuit and/or while housing the pump in a very small space.

For this, it is advantageous to use pumps having swashplates and axial pistons.

Hydraulic pumps having an inclined plate, or swashplate, which actuates axial pistons have been known for a very long time.

In particular, the use of hollow pistons is known, which pistons press against a swashplate by means of slipper shoes through which each piston is supplied with liquid when its slipper shoe passes over an arcuate opening, known as a crescent, cut into the face of the swashplate; the liquid thus aspirated into the hollow piston is discharged through a check valve arranged at the end of the cylinder inside which the piston slides.

For this type of pump, the use of what is termed valve plate distribution is known, wherein the pistons are carried by a barrel driven in rotation and the rear face of said barrel is pressed by a spring against a valve plate consisting of a disk having arcuate perforations.

However, it turns out that this technique, which is widely used by the applicant, cannot be used for pumps having a displacement of less than 4 to 5 cm³ because, in that case, in order to avoid the discharge pressure separating the rear face of the barrel from the distribution valve plate, it is necessary for said crescents to have such a small cross section that it is impossible in practice to machine them. Moreover, the very small size of the crescents greatly reduces the suction of the pump, which is not necessarily compatible with the desired application of the pump.

The present invention relates to an axial piston pump able to provide an output in both directions of rotation and which is suitable for very small displacements, it being possible for the displacement of this pump to be of the order of 40 mm³ or even less.

According to the present invention, the pump comprises a casing, a common drive shaft mounted so as to be able to rotate relative to the casing, two swashplates borne by the common drive shaft, these two swashplates being symmetric and opposite each other and each comprising one supply crescent, a respective hollow piston pressing against each swashplate via the intermediary of a slipper shoe and designed to slide in a respective cylinder connected to the casing, the crescent of the swashplate being in each case arranged so as to pass over the hollow piston during a suction phase of the hollow piston, each cylinder being fitted with a check valve on the discharge side, such that only one of the two swashplates provides an output when the drive shaft rotates in one direction, the other swashplate providing an output when the shaft rotates in the other direction; this makes it possible to produce a pump of very small displacement delivering an output at one of the pump's two discharge openings, depending on the direction of rotation of the pump.

The pump preferably comprises two separate discharge openings, one for each output, as well as one check valve per pump piston.

According to one embodiment, the hydraulic pump comprises two discharge openings, one discharging the liquid pressurized by one of the swashplates, the other discharging the liquid pressurized by the other swashplate; liquid is supplied either through a supply opening which opens into the space where one or other of the swashplates is oscillating, or through the rolling bearings which carry said swashplates.

The present invention will be more easily understood with reference to the appended drawings, in which:

FIG. 1 is a view in longitudinal section of an exemplary embodiment of a pump having a displacement of for example less than 40 mm³ and able to provide an output depending on the direction of rotation of the pump.

FIG. 2 is a plan view of the first swashplate of the pump of FIG. 1, having a crescent which is cut for rotation in the clockwise direction.

FIG. 3 is a plan view of the second swashplate of the pump of FIG. 1, having a crescent which is cut for rotation in the counterclockwise direction.

FIGS. 1 to 3 show an embodiment of the invention which is in particular intended for pumps having very small displacements.

With reference to these figures, it can be seen that the drive shaft 100 carries two swashplates 101 and 102 which are symmetric and have opposite slopes, each one comprising a single crescent 106 and 107 which are in diametrically opposite positions. Pistons 103 are held pressed against the swashplate 101 by springs 104 via the intermediary of slipper shoes 105. In analogous fashion, pistons 103 are held pressed against the plate 102 by springs 104 and via the intermediary of the slipper shoes 105. The plate 101 rotates in a chamber 112 filled with hydraulic liquid and the plate 102 rotates in an analogous chamber 113. The liquid discharged under pressure by the action of the pistons actuated by the plate 101 passes through the check valve 108 and exits through the opening 110. In analogous fashion, the liquid discharged under pressure by the action of the plate 102 passes through the check valve 109 and exits through the opening 111.

Thus, when the shaft 100 rotates in the clockwise direction, it is the plate 101 that provides the output (FIG. 2) and when the shaft 100 rotates in the counterclockwise direction, it is the plate 102 that provides the output (FIG. 3).

It is thus possible to have a pump of very small displacement capable of discharging depending on the direction of rotation of the pump.

In operation, the pump is designed to be submerged in a reservoir of hydraulic liquid, for example inside an oil drilling tube. The chambers 112 and 113 fill with hydraulic liquid either through perforations (not shown) in the pump casing which open into these chambers or through the rolling bearings carrying the shaft 100.

Use of the verb “comprise”, “possess” or “include” and the conjugated forms thereof does not preclude the presence of elements or steps other than those disclosed in a claim. The use of the indefinite article “a” or “one” for an element does not preclude, unless otherwise stated, the presence of a plurality of such elements.

In the claims, in no way can a reference sign between parentheses be interpreted as a limitation of the claim. 

1. A hydraulic pump which rotates in both directions, and which comprises a casing, a common drive shaft mounted so as to be able to rotate relative to the casing, two swashplates borne by the common drive shaft, these two swashplates being symmetric and opposite each other and each comprising one supply crescent, a respective hollow piston pressing against each swashplate via the intermediary of a slipper shoe and designed to slide in a respective cylinder connected to the casing, the crescent of the swashplate being in each case arranged so as to pass over the hollow piston during a suction phase of the hollow piston, each cylinder being fitted with a check valve on the discharge side, such that only one of the two swashplates provides an output when the drive shaft rotates in one direction, the other swashplate providing an output when the shaft rotates in the other direction.
 2. The hydraulic pump as claimed in claim 1, comprising two discharge openings, one discharging the liquid pressurized by one of the swashplates, the other discharging the liquid pressurized by the other swashplate depending on the direction of rotation of the shaft.
 3. The hydraulic pump as claimed in claim 1, comprising at least one supply opening which opens into at least one of the chambers in which the swashplates oscillate.
 4. The hydraulic pump as claimed in claim 1, wherein the supply liquid passes through one or other of the rolling bearings carrying the shaft which carries the swashplates.
 5. The hydraulic pump as claimed in claim 2, comprising at least one supply opening which opens into at least one of the chambers in which the swashplates oscillate.
 6. The hydraulic pump as claimed in claim 2, wherein the supply liquid passes through one or other of the rolling bearings carrying the shaft which carries the swashplates. 